Historically, transition metal complexes containing isonitrile ligands have been limited to those containing the few commercially available isonitriles like t-BuNC and PhNC or to the readily synthesized and purified isonitriles like MeNC, EtPhNC, MeOPhNC, and MePhNC, wherein t-Bu=tertiary butyl, Ph=phenyl, Et=ethyl, and Me=methyl. For a review see: Bonati, F.; Minghetti, G. Inorg. Chim. Acta 1974, 9, 95-112. Only recently have complexes containing more `exotic` isonitriles been studies (Winzenburg, M. L.; Kargol, J. A.; Angelici, R. J. J. Organomet. Chem. 1983, 249, 415-428).
Salts of the type [L.sub.4 M][M'X.sub.4 ] are known as double-complex salts, i.e. the salt is composed of two metal-containing complex ions. Salts where L is an amine or isonitrile, X is a halide or cyanide, and both M and M' are platinum have been known for many years. For a recent review of metal isocyanide complexes see: Singleton. E; Oosthuizen, H. E. Adv. Organomet. Chem. 1983, 22, 209-238. Both the cation and anion in these complexes have square-planar geometries and often assume structures in which the ions form mixed stacks; the resulting metal-metal interactions cause these solids to be intensely colored despite the fact that the component ions absorb below 350 nanometers (nm) (Bonati, F.; Minghetti, G. J. Organomet. Chem. 1970, 24, 251; Isci, H. and Mason, W. R. Inorg. Chem. 1975, 14, 913; Mason; W. R.; Gray, H. B. J. Am. Chem. Soc. 1968, 90, 5721). A study of the optical properties of these salts is reported by Isci and Mason (Inorg. Chem. 1974, 13, 1175-1180). Simple salts having cations of the type [(RNC).sub.4 M].sup.n+ where M includes radioactive isotopes of Rh(n=1) and Ni, Pd, or Pt(n=2), and R is an organic radical are described in U.S. Pat. No. 4,452,774 for use as diagnostic agents for labeling living cells. U.S. Pat. No. 4,271,033 discloses binucleating biisocyanide complexes of Rh, Pt, Pd, and Ni useful as catalysts. Isonitrile or isocyanide complexes of copper, described in U.S. Pat. No. 3,197,493, are useful as intermediates in the preparation of isonitriles.
U.S. Pat. No. 4,130,432 claims alkyl tin tetracyanometallates as biocides. Double salts of tetracyanoaurate useful for plating gold alloys are disclosed in U.S. Pat. No. 3,458,542. Tetrahalonickelates useful as catalysts are taught in U.S. Pat. No. 2,738,364.